This invention relates generally to apparatus and methods for calibrating measuring devices and particularly, but not by way of limitation, to apparatus and methods for calibrating a flowmeter which includes a body and an electromagnetic member disposed in the body.
To measure a parameter with a measuring device, the parameter causes the measuring device to generate a measurement signal which is used to drive a display of the measuring device whereby the measure of the parameter is made known to an observer. By way of example, consider a fluid flowing through a pipe. The operator who is flowing the fluid commonly desires to measure how much of the fluid is flowing or has flowed. To make such a measurement, a flowmeter can be inserted in line with the pipe so that the flowing fluid impinges on a rotor of the flowmeter, thereby rotating the rotor and causing electrical pulses to be generated in a known manner within the flowmeter. Using an internal calibration factor, the flowmeter converts the number of pulses into the corresponding quantity of fluid and displays that quantity through the display.
As is readily apparent, the accuracy of the displayed value depends, at least in part, on the correctness of the calibration factor. The accuracy also depends on the stability of the electrical and mechanical operation of the flowmeter. Thus, if the electrical or mechanical operation changes, the calibration factor must also be changed to compensate for these other changes. Furthermore, for the specific example of a flowmeter, the correctness of the calibration factor can vary depending upon the type of fluid to be measured, or the plumbing configuration of the fluid circuit into which the flowmeter is connected, or the turbulence of the flow, or the presence of air in the fluid. Whatever the reason, however, it is apparent that to maintain an accurately operating measuring device, such as a flowmeter, one must be able to calibrate the device as needed. That is, one must be able to reset or adjust the calibration factor by which the measuring device correlates the measurement signal it generates to the actual parameter.
With respect to the example of a flowmeter, there is at least one type of slowmeter which can be internally calibrated by flowing a known quantity of fluid through the flowmeter. This type of calibration can, however, be an undesirable technique when, for example, the fluid is expensive or hazardous whereby one does not want to use the fluid merely for calibrating.
Again with respect to the example of a flowmeter, there is at least one type of flowmeter which has an ability to internally calibrate itself within certain preset data or controls contained in the flowmeter. Such preset data, however, do not encompass all the various changes to the calibration factor which a user of the flowmeter may wish to make. For example, the preset data may pertain only to a factory standard calibration which is optimum for only one type of fluid, whereas the flowmeter itself could be used to measure other types of fluids if the flowmeter could be optimally calibrated to such other types. Although such a flowmeter could be removed from the fluid circuit and rebuilt or reprogrammed or otherwise modified as needed to input the desired calibration factor, such removal may be impractical or otherwise undesirable for a specific application of the flowmeter (e.g., if the flowmeter has been permanently plumbed into the fluid circuit).
To overcome these specific exemplary shortcomings, there is the need for an apparatus and a method for calibrating such a flowmeter without having to create an actual flow of the fluid for which the calibration is to be made and without having to remove the flowmeter from the fluid circuit. It is contemplated that other types of measuring devices can be calibrated by a comparable apparatus and method; therefore, more broadly, there is the need for an improved apparatus and method for calibrating measuring devices whereby the actual parameter to be measured need not be used and whereby the measuring device can be calibrated in situ (i.e., at the location where it is to do its measuring).